Heat shock protein 90 (HSP90) is an intracellular chaperone protein that assists protein folding, stabilizes proteins against heat stress, and aids in protein degradation. It is upregulated in many types of cancer. Many Hsp90 client proteins are over-expressed in cancer, often in mutated forms, and are responsible for unrestricted cancer cell proliferation and survival. HSP90 derived from tumour cells has higher binding affinity to HSP90 inhibitors than the latent form in normal cells, allowing specific targeting of HSP90 inhibitors to tumour cells with little inhibition of HSP90 function in normal cells. Further, HSP90 has also been recently identified as an important extracellular mediator for tumour invasion. Therefore, HSP90 is considered a major therapeutic target for anticancer drug development.
Nanoparticulate drug delivery systems are attractive for systemic drug delivery because they may be able to prolong the half-life of a drug in circulation, reduce non-specific uptake of a drug, and improve accumulation of a drug at tumors, e.g., through an enhanced permeation and retention (EPR) effect. There are limited examples of therapeutics formulated for delivery as nanoparticles, which include DOXIL® (liposomal encapsulated doxyrubicin) and ABRAXANE® (albumin bound paclitaxel nanoparticles).
The development of nanotechnologies for effective delivery of drugs or drug candidates to specific diseased cells and tissues, e.g., to cancer cells, in specific organs or tissues, in a temporospatially regulated manner potentially can overcome or ameliorate therapeutic challenges, such as systemic toxicity. However, while targeting of the delivery system may preferentially deliver drug to a site where therapy is needed, the drug released from the nanoparticle may not for example, remain in the region of the targeted cells in efficacious amounts or may not remain in the circulation in a relatively non-toxic state for a sufficient amount of time to decrease the frequency of treatment or permit a lower amount of drug to be administered while still achieving a therapeutic effect. Accordingly, there is a need in the art for improved drug targeting and delivery, including identification of targeting molecules that can be incorporated into particles and whose presence does not substantially interfere with efficacy of the drug.